Validation is always nice, even if it comes from people whose opinions you don't value. It can be relieving to hear family members finally acknowledge your experience after a lifetime of invalidation and ignoring the reality of the situation.
I'm sorry that you not only had to endure growing up with an addicted mother, but that the other adults in your life were complacent. Just like it takes a village to raise a child, it takes a village to neglect and abuse a child. Mistreatment of children doesn't happen in a vacuum. There is always someone who knows, and then chooses to look the other way.